Remyelination in the CNS requires oligodendrocyte progenitor cells (OPCs) to divide and migrate towards areas of damage. Some cell migration does occur, but it ultimately ceases and is inadequate. Molecular strategies aimed at promoting post-injury migration of endogenous OPCs could thus improve myelin repair. In the brain, the endothelin (ETs) peptides are synthesized by endothelial cells, neurons and astrocytes. ETs, in particular ET-1, have been implicated in astrocyte and Schwann cell proliferation and maturation; however, their biological effects on oligodendrocyte development are unknown. In both cultured cells and in tissue slices, we will test the hypothesis that ET-1 regulates oligodendrocyte development, namely OPC proliferation, migration and differentiation. Our preliminary results using an in vitro assay indicate that ET-1 promotes OPC migration, but does not affect cell proliferation. We therefore propose to pursue the following avenues of investigation: first, we will establish whether expression of the two main ET-receptors (ET-Rs) found in the brain, ETA-R and ETB-R, is developmentally regulated in cells of the oligodendrocyte lineage in culture and in vivo. With selective ET-R antagonists, we will also define the main signal transduction pathways associated with ETA and ETB-R-activation in OPCs, and their contribution to the activation of specific transcription factor targets. We will investigate the protein kinase C (PKC), extracellular signal-regulated kinase (ERK), and p38-mitogen-activated protein kinase (MAPK) pathways. Second, we will identify the ET-R subtype(s) mediating the functional effects of ET-1 on OPC migration, and define the influence of ET-1 on OPC differentiation. Third, we will extend our studies performed in culture to a more intact system. We will apply multiphoton microscopy to analyze the role of the ET system in OPC proliferation and migration in postnatal brain slices prepared from mice expressing the green fluorescent protein in cells of the oligodendrocyte lineage. Our aim is to define signals that promote OP cell migration and repopulation of demyelinated areas. Our studies will: i) define a role for ET-1 and ET-Rs as migratory signals in oligodendrocyte development, and ii) determine whether novel means of enhancing OP migration could be explored to facilitate myelin repair.